This invention relates to a method of making heat exchangers, and particularly to a method of making annular tube-fin heat exchangers.
The prior art known to me which is most pertinent to my invention is that represented by the disclosures in:
1. Brown Fintube Company, British Pat. No. 692,885, published June 17, 1953; and
2. Samuel J. DeMarco, U.S. Pat. No. 3,636,607, issued Jan. 25, 1972.
The disclosure of the British patent is pertinent because it is concerned with a heat exchanger comprised of concentric tubes and inserted "packing" material, tube surfaces and packing material being bonded together. The deficiencies of the British patent disclosure, insofar as the present invention is concerned, lie in a method of assembly which utilizes a preparation for bonding by tube expansion and which utilizes a technique for closing tube ends not involving the tube expansion step. The method of making of the British patent accordingly is inherently slow and not well suited to large scale production. The tube expansion process is, moreover, not one best calculated to achieve minimal contact resistance between the "packing" material and the tube wall. Gaps in continuing joints between the "packing" material and the tube walls produce non-uniform heat transfer effects. A closing of tube ends only as a part of the bonding step, and after tubes have been expanded, fails to take into account tolerance differences and variations in tube expansion which may occur, and as a result will normally involve after-fabrication sealing of gaps and crevices.
The disclosure of the United States patent is pertinent because it teaches a method of making a heat exchange tube in which an inserted fin annulus is compressed in a tube for low contact resistance by a process of electromagnetically deforming the tube radially inwardly. The deficiencies of the United States patent, insofar as its pertinence to the present invention is concerned, lie in a method of assembly which electromagnetically deforms a single tube radially inwardly toward a rigid central support but which does not teach that a tube assembly so formed may be used as the rigid central support in the deforming of another tube and that this may be used as the core of a still further tube and so on. Neither does the United States patent teach anything in regard to closing of the tube ends so that the several defined fluid flow paths may be used in effecting heat transfer between plural confined fluids. The United States patent deals with electromagnetic tube forming and is in no sense defective or incomplete in its disclosure. The concern of the present invention is with matters not taken up in the United States patent and which may be regarded as beyond the scope of the teachings of that patent.